Car Loan Payment Calculator: Estimate Monthly Costs

A car loan payment calculator estimates your fixed monthly principal-and-interest payment from the amount borrowed, annual percentage rate (APR), and loan term. Enter those three figures to see the monthly payment and the total interest implied by the calculator’s rounded payments.

Formula

The calculator uses the standard fixed-payment loan formula. It converts APR to a monthly rate, calculates the payment that amortizes the balance over the selected number of monthly payments, and rounds that payment to the nearest cent:

Monthly payment = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]

• P is the amount financed, in dollars.
• r is the monthly interest rate, calculated as APR ÷ 1,200. For example, 8% APR gives a monthly rate of 0.0066667.
• n is the number of monthly payments, calculated as the loan term in years × 12.
• round(…, 2) rounds the payment to cents.

Total interest is estimated as rounded monthly payment × n − P. Because this uses the payment rounded to cents, it reflects the calculator’s consistent-payment estimate; a lender’s final payment may be adjusted slightly to settle the remaining balance.

Worked Example

Using the calculator’s default inputs—$20,000 financed, 8% APR, and a five-year term—the monthly rate is 8 ÷ 1,200 = 0.0066667, and the number of payments is 5 × 12 = 60.

1. Calculate the payment factor: 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
2. The unrounded payment is approximately $405.53.
3. Rounded to cents, the monthly payment is $405.53.
4. Total interest using the rounded payment is $405.53 × 60 − $20,000 = $4,331.80.

The corresponding total of the 60 estimated payments is $24,331.80, including the original $20,000 principal and $4,331.80 in estimated interest.

Assumptions

• The interest rate remains fixed for the full term.
• Payments are equal monthly payments made at the end of each monthly period.
• Interest accrues monthly using APR divided by 12; this calculator treats the APR as a nominal annual rate.
• The estimate excludes taxes, registration, insurance, fees, optional products, and any down payment or trade-in unless those amounts are already reflected in the loan amount.

What to Enter and How to Read the Result

Loan amount means the principal actually financed, not necessarily the vehicle’s advertised price. A down payment or trade-in value may reduce the amount borrowed, while taxes, fees, or other items included in financing may increase it. Use the amount shown in the lender’s proposed loan details if available.

APR is entered as an annual percentage, so enter 8 for 8%, not 0.08. The APR is an input, not a quote or prediction. Obtain the applicable figure and the amount financed from the lender’s written disclosure. This calculator does not infer a rate from a credit profile or vehicle price.

Term is entered in years. The formula converts it to months: five years means 60 payments. The result is only the loan payment for principal and interest. It is not a complete estimate of vehicle ownership costs or a decision about whether a payment fits a particular budget.

How Loan Term and Down Payment Affect the Estimate

For the same principal and APR, extending the term generally lowers the required monthly payment because repayment is spread across more months. However, interest accrues for a longer period, so the total interest is generally higher. A shorter term generally raises the monthly payment while reducing the number of periods over which interest accumulates. Compare both outputs rather than looking at the monthly amount alone.

A larger down payment generally means a smaller principal if the vehicle price and other financed costs stay the same. For example, reducing the amount financed changes P in the formula; it does not automatically change APR or term. A trade-in can have the same arithmetic effect if its value is applied to reduce the principal, but the calculator does not estimate a trade-in’s value or account for any outstanding balance on it.

Common Calculation Mistakes and Limits

• Mixing percent formats: The input is APR as a percent, such as 8, and the formula divides by 1,200 to convert it to a monthly decimal rate.
• Entering vehicle price instead of amount financed: The amount financed can differ after a down payment, trade-in, taxes, fees, or other items.
• Confusing payment with total cost: The monthly result excludes ongoing ownership costs such as insurance, fuel, maintenance, and registration.
• Assuming every contract has identical timing: Actual payment dates, daily interest calculations, fees, or a final adjusted payment can make lender figures differ from this standard monthly model.

The formula assumes a fixed rate and equal monthly installments. It does not model variable rates, skipped or late payments, extra principal payments, a balloon payment, or a changing balance caused by fees. It also does not determine whether a loan application will be approved or what rate a lender will offer.

Frequently Asked Questions

How do I calculate a car loan payment by hand?
Convert APR to a monthly decimal rate by dividing the percentage by 1,200, and convert the term to months. Substitute the principal, monthly rate, and number of payments into P × r ÷ [1 − (1 + r)⁻ⁿ], then round the result to cents.

Does a car payment calculator include insurance and taxes?
Not in this calculation. It estimates principal and interest only. Add any relevant insurance, taxes, or other costs separately when making a broader budget estimate; their amounts are not calculated here.

Why is my lender’s payment slightly different?
The lender may use different payment dates, day-count conventions, fees, financed items, or rounding. The contract may also adjust the final installment. Compare the calculator’s inputs with the lender’s disclosed amount financed, APR, term, and payment schedule.

Does a longer loan term reduce total interest?
For the same principal and fixed APR, a longer term usually lowers each monthly payment but increases total interest because the balance is repaid over more periods. The precise estimate depends on the entered figures and payment schedule.

Can I use this calculator to include a down payment?
Yes. Subtract the down payment and any trade-in amount applied to the purchase from the price, then account for other costs included in financing. Enter the resulting amount financed as the loan amount. This tool does not calculate those transaction amounts for you.

This result is an estimate; the lender’s disclosure gives the exact figures.

Related

• Auto Loan Calculator With Trade-In and Amount Owed (Negative Equity)
• Car Loan Calculator With Down Payment: Monthly Car Payment

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2